The invention relates to a method of manufacturing a textured, multi-layered, mold-formed body, with a top foil containing partially crosslinked polymer materials based in particular on polyolefins and in some cases containing further additives, and with at least one sub-foil laminated to the top foil, wherein the foil laminate is embossed with a texture and then treated with electron beams to stabilize the texture sufficiently for a deep-drawing process, and wherein the treated foil laminate is deep-drawn to produce a textured, multi-layered, mold-formed body.
The invention further relates to a method of manufacturing a textured mold-formed body with a plurality of layers, with a top foil that contains partially crosslinked polymer materials based in particular on polyolefins and in some cases contains further additives, and with at least one sub-foil laminated to the top foil, wherein the foil laminate is treated with electron beams and the treated textured foil laminate is processed further into a mold-formed body.
Furthermore, the invention also relates to carrier-supported, textured, mold-formed bodies with a plurality of layers that are made in the manner described above, and it also relates to the use of the mold-formed bodies for the interior linings of motor vehicles.
In the fields of automotive technology and of technical foil products there has been a strong tendency over a number of years to replace the widely used PVC materials with halogen-free substances. Polyolefins represent a widely used class of materials that can serve as substitutes for PVC materials in automobile interiors. With suitable polymerization techniques, a wide variety of material property profiles are achievable in polyolefins. For example with specifically targeted polymerization processes it is possible to produce extremely rigid high-crystalline polypropylene types that remain stable under temperatures up to 150° C. On the other hand, by copolymerizing the propylene with other monomers it is also possible to synthesize rubber-like polypropylenes, albeit with a totally inadequate shape stability.
The European Patent EP 01 106 354 deals with decorative foils on polyolefin basis for applications in automobile interiors. Critically important factors in this field include stability of the texture, homogeneity of the texture after the forming process, haptics (tactile feel), freedom from aging effects, colorfastness, emissions and the like. A method is described in EP 01 106 354 for the manufacture of a textured mold-formed body containing partially crosslinked polyolefins and in some cases further additives. In a first stage, a foil is produced from non-crosslinked polyolefins and in some cases further additives. This foil is embossed and then treated with electron beams in order to achieve an adequate stability of the texture for a deep-drawing process. The treated foil is subsequently deep-drawn to produce a mold-formed body with a textured surface. Also mentioned in EP 01 106 354 is the possibility to laminate the foil in its irradiated or non-irradiated condition to produce a laminar compound. The foil according to this known state of the art is distinguished by the fact that the electron-beam irradiation after the embossing has a desirable crosslinking effect which results in a highly stable texture after the deep-drawing process. The laminated foil of this known state of the art is particularly important for automobile interiors.
There is a notable trend in the automotive supplier industry to also use so-called direct-laminating processes in an effort to gain efficiency in the production of parts for automobile interiors. The term direct-laminating refers in general to processes in which the lining part is produced in a single process step from a decorative foil and a carrier material without an adhesive system. Examples of these techniques are the press-laminating process, the fused deposition modeling process, or the in-mold decoration process. Processes of this type are described for example in EP 0 968 806 A1, EP 0 730 947 B1, EP 0 650 828 B1, as well as DE 196 18 393 A1.
Unlike the standard deep-drawing processes used in the manufacture of surface decor parts for automobile interiors, some of the direct-laminating processes are distinguished by the fact that the step of shaping the part simultaneously includes the formation of the carrier part over the backside of the foil. In the customary deep-drawing process, the three-dimensionally preformed carrier is press-formed or extruded with the desired contour shape in a preceding separate production step. The carrier is subsequently coated with an adhesive. In the deep-drawing process, the adhesive reacts with an adhesion-promoting lacquer that has been applied to the backside of the foil. In order to ensure the activation of the adhesive, it is in some cases necessary to raise the temperature above a defined activation temperature of the adhesive.
In the direct-laminating process, the carrier material is preheated to a certain temperature and placed into the forming tool together with the foil. The carrier-supported textured mold-formed body is produced in a press-forming operation in which the decorative foil as well as the carrier receive their desired three-dimensional shape. This saves in many cases the separate steps of producing the carrier as well as applying the adhesive. Also, it is no longer necessary to apply the adhesion-promoting lacquer to the backside of the foil. Also, because of the mutually matched combination of decorative foil material and carrier material, the direct-laminating process avoids the problem of a weakening of the adhesive which occurs occasionally, particularly after a certain aging period, and which can lead to rejected production parts due to a partial peeling of the foil from the carrier. It is normally a special trait of the forming operations according to the direct-laminating principle that, unlike in the deep-drawing process, the face side of the decorative material that enters into the forming process does not necessarily have to be heated separately in the final shaping stage. A problem that can occur with foils of conventional composition as used in deep-drawing applications is associated with the low process temperatures on the face side of the decorative foil, as portions of the decorative foil that were subjected to a higher degree of stretching in the forming process may afterwards exhibit white or gray areas that are known as “white breaks”. In an attempt to avoid the symptom of white breaks, soft components are normally added to the formulation of the base material for the foil. However, this reduces the shape stability in hot environments, the abrasion resistance, and the stability of the texture after the shaping operation.
In order to achieve a pleasing tactile feel or a desired haptic property in decorative foils, a foam is often applied to the backside of the foil. In addition to the improved haptic properties that can thereby be achieved, the foam simultaneously takes on a protective function for the decorative foil in direct-laminating processes as a shield against the carrier material that is pressed onto the backside of the foil. Therefore, the foam that is used in these processes also needs to have a sufficient thermal and mechanical stability so that it will not collapse over large surface areas when it comes into contact with the carrier material which may have been heated up to 240° C. If this kind of collapse occurs, there is a significantly greater risk that the carrier material escapes through the top foil or that the texture is flattened to an unacceptably high degree.
The materials used in polyolefinic decorative foils are primarily polyolefin foams based on polyethylene and/or polypropylene. In their manufacturing process, these foams are normally crosslinked by means of electron beams. Polypropylene in particular, but also polyethylene, have a known tendency to decompose under the influence of electron beams. The extent of the decomposition increases with a larger dose of radiation. Therefore, if the use of a crosslinking treatment by electron-beam irradiation is being considered after the embossing in order to improve the stability of the texture of the top foil of a foil laminate, one has to assume that this will negatively affect the mechanical properties of the foam because of the decomposition of the polymers. At the same time, the foam will lose some of its protective function for the decorative foil.